Process for nitrating non-aromatic



PROCESS F OR NITRATING NON AROMATIC HYDROCARBUNS Jack H. Krause, Media, and Robert K. Smith, Springfield,

Pa., assignors to Houdry Process (Iorporation, Wilmiugton, DeL, a corporation of Delaware No Drawing. Application November 8, 1955 Serial No. 545,776

3 Claims. (Cl. 260--644) The present invention relates to the nitration of nonaromatic hydrocarbons, and more particularly to the nitration of non-aromatic cycloparalfins having five or more carbon atoms, and including a secondary or tertiary carbon atom.

In recent years many uses have been developed for the nitro derivatives of non-aromatic hydrocarbons. Thus, l-nitro-1-methylcyclopentane is an excellent solvent for lacquers, resins, polymers, and as a useful chemical intermediate, etc. Other nitro derivatives of non-aromatic hydrocarbons have likewise been utilized for solvents, organic intermediates, etc.

Low molecular weight hydrocarbons, such as aliphatic hydrocarbons having from one to four carbon atoms, have been successfully nitrated with nitric acid, or with oxides of nitrogen in the vapor phase. This technique has found wide utility with such hydrocarbons and is presently being practiced on a large scale. However, vapor phase nitration has not proved successful with higher molecular weight hydrocarbons. Thus, higher molecular weight hydrocarbons, such as hydrocarbons having five or more carbon atoms, are excessively oxidized and dissociated when contacted with nitric acid or oxides of nitrogen in the vapor phase, so that unsatisfactory yields of nitro compounds are obtained under these conditions.

Liquid phase nitration has proved to be substantially inefiective with non-aromatic hydrocarbons having five or more carbon atoms with nitric acid solutions of 20 weight percent nitric acid strength or less. More concentrated solutions of nitric acid produce excessive oxidation of the hydrocarbons with poor conversion to nitro derivatives.

The use of solid nitrate salts as nitrating agents-for the nitration of non-aromatic hydrocarbons has been contemplated but has not proved to be satisfactory. Thus, when aluminum nitrate nonahydrate (Al(NO 9H O) has been used as a nitrating agent, particularly in the nitration of cycloparaffins, the nitration proceeded with excessive dissociation, usually resulting in a violent and uncontrollable reaction.

This invention has as an object the provision of a process for nitrating non-aromatic hydrocarbons, and in particular, cycloparafiins having five or more carbon atoms to form mononitro derivatives.

This invention has as a further object the provision of a process for nitrating non-aromatic hydrocarbons having five or more carbon atoms and having a secondary or tertiary carbon atom.

This invention has as yet another object the provision of a method for selectively nitratiug a non-aromatic hydrocarbon of at least five carbon atoms and having a tertiary carbon atom in a mixture of hydrocarbons of similar molecular weight having primary or secondary carbon atoms.

2,864,87 Patented Dec. 16, 1958 This invention has as a further object the provision of a selective chemical conversion method whereby a mixture containing a non-aromatic hydrocarbon of five or more carbon atoms and a secondary carbon atom and a non-aromatic hydrocarbon of similar molecular weight and having a tertiary carbon atom are selectively converted to yield respectively a ketone derivative and a nitro derivative.

These and other objects are accomplished by the process of the present invention wherein a non-aromatic hydrocarbon having five or more carbon atoms is nitrated, as at an elevated temperature, such as a temperature of about 220 F. to 280 F. and preferably 240 F. to 260 F. through contact with aluminum nitrate nonahydrate containing between about five to thirty weight percent of unbound water, that is water over and above the so-called water of crystallization or bound water in the hydrate. The relative molar ratio of aluminum nitrate nonahydrate to hydrocarbon should be between 0.5 to 3.0, and preferably from 1 to 2 moles per mole of hydrocarbon.

The nitration process of the present invention is primarily applicable to non-aromatic hydrocarbons having from five to twenty carbon atoms and containing a secondary or tertiary carbon atom. It has been found that the reactivity of the hydrocarbons, especially cycloparaflins, in the process of the present invention is dependent upon the presence of a tertiary or secondary carbon to hydrogen bond, which are designated tertiary and secondary carbon atoms respectively, and that compounds having a tertiary carbon atom are far more reactive than those having a secondary carbon atom. In fact, compounds having a tertiary carbon atom may be so reactive as to be prone to go beyond the formation of mononitro derivatives and to form polynitro derivatives and oxidation or dissociation products. With such highly reactive compounds, it is desirable to efiect nitration in the presence of hydrocarbon diluentssuch as the normal paraffins, like normal heptane or a paraflinic naphtha. Where highly reactive hydrocarbons containing a tertiary carbon atom are nitrated in the presence of hydrocarbons containing a secondary carbon atom, nitration of both types of hydrocarbons may be encountered, with the nitration of the compound having a tertiary carbon atom predominating.

The separation of mononitro derivatives of non-aromatic hydrocarbons having a tertiary carbon atom from similar derivatives of similar type hydrocarbons having a secondary carbon atom may be readily accomplished by contacting the nitrated mixture with a solution of hot concentrated sodium hydroxide or other strong alkali. Such contact will readily convert the mononitro derivative containing a secondary carbon atom into the Water-soluble sodium salt of the pseudo acid or so-called aci-form. The mononitro derivative having a tertiary carbon atom is insoluble in aqueous alkali and can be readily separated therefrom. Acidification of the alkaline solution containing the soluble sodium salt of the pseudo acid will yield the ketone derivative of the hydrocarbon having a secondary carbon atom.

A preferred embodiment of the nitration process of the present invention constitutes the nitration of cycloparafiins to form the nitro derivatives of such cycloparafiins. Thus, methylcyclopentane, a cycloparafiin having a tertiary carbon atom may be nitrated in accordance with the present invention to yield l-nitro-l-methylcyclopentane.

Cyclohexane, a cycloparafiin having six secondary carbon atoms may be nitrated to yield nitrocyclohexane, which in turn may be converted to the soluble sodium aseasro salt of aci-nitrocyclohexane by contact with hot concentrated sodium hydroxide solution.

This water-soluble sodium salt may be converted into cyclohexanone upon acidification of the sodium hydroxide solution. The cyclohexanone may be oxidized in the presence of a suitable oxidizing agent, such as nitric acid, to yield adipic acid which may be used in the manufacture of long chain polyamide polymers, such as nylon made by E. I. Du Pont de Nemours and Company of Wilmington, Delware, which is a copolymer of adipic acid and hexamethylene diamine.

As both methylcyclopentane and cyclohexane may be present in appreciable quantities in petroleum, frequently in admixture with each other, the process of the present invention constitutes a facile method for preparing the aforementioned products. It is advantageous to efi ect the nitration of methylcyclopentane in the presence of cyclohexane, since, as heretofore noted, methylcyclopentane is highly reactive due. to its tertiary carbon atom, and improved: yields ofits mononitro derivative may be obtained when it is nitrated in the presence of a less reactive cycloparafiin, such as cyclohexane, containing a secondary carbon atom.

The convenient and facile separation of the nitration products may be accomplished by forming the soluble sodium salt derivative of the aci-form of nitrocyclohexane as above noted.

The process of the present invention may be applied to a wide variety of cycloparaflins including by Way of example in addition to cyclohexane, cyclopentane, cycloheptane, cyclooctane, decalin, etc.

The process of the present invention is also applicable to a wide variety of non-aromatic hydrocarbons having five or more carbon atoms such as terpene hydrocarbons, like menthene, camphene, pinene, etc.; alkylated aromatic compounds; branched-chain paraffins, like the branchedchain dodecanes which are obtained from the commercial process designated alkylation involving the conversion of mixtures of isobutane and butene to a product containing branched-chain dodecanes, 2,3-dimethyl butane; alkyl-aromatic compounds such as cumene; etc.

As illustrative of the process of the present invention, the nitration of methylcyclopentane to nitromethylcyclopentane was effected under a variety of conditions as will be apparent from the following exarnples;

Example I The nitration of 1.5 moles methylcyclopentane using 1 mole of aluminum nitrate nonahydrate and weight percent of water based on the aluminum nitrate nonahydrate at a temperature of 240 to 250 F., a reaction time of 150 minutesabove 220 F., and a maximum developed pressure of 600 pounds per square inch gauge yielded of theory of nitromethylcyclopentane.

The conversion of methylcyclopentane was 37 weight percent, and the selectivity of conversion to nitromethylcyclopentane was 41 percent (by selectivity is meant the yield based on theory divided by the conversion multiplied by 100 Example II The nitration of a mixture of 33 weight percent normal heptane and 67 weight percent methylcyclopentane using aluminum nitrate. nonahydrate and weight percent of water based on the aluminum nitrate nonahydrate, with the molar ratio of the heptane and methylcyclopentane to the aluminum nitrate nonahydrate being 1.5, at-aternperature of 250 to 255 F., areaction time of 3 hours above 220 F., and a maximum developed pressure of 675 pounds per square inch gauge yielded 20% of theory of nitromethylcyclopentane.

Theconversion of methylcyclopentane was- 54 weight percent, andtheselectivityof conversion to nitromet yr cyclopentane was 37 percent.

4 Example III The nitration of a mixture of 57 weight percent methylcyclopentane, 27 weight percent cyclohexane, 9 weight percent of a mixture of parafiins containing six and seven carbon atoms, and 3 weight percent benzene using aluminum nitrate nonahydrate and 20 weight percent of water based on the aluminum nitrate nonahydrate, with the molar ratio of the hydrocarbons to the aluminum nitrate nonahydrate being 2.1, at a temperature of 240 to 260 F., a reaction time of 180 minutes above 220 F., and a maximum developed pressure of 700 pounds per square inch gauge yielded 29% of theory of nitromethylcyclopentane.

The conversion of methylcyclopentane was 58 weight percent, and the selectivity of conversion to nitromethylcyclopentane was 49 percent.

The nitration of methylcyclopentane has been studied using nitric acid as a nitrating agent and also using aluminum nitrate nonahydrate in the absence of water. The results obtained from this study are presented in the following table:

1 Methylcyclopentane. 1 Based on nitrating agent. I

It will be seen from comparing the examples with the results set forth in the table that aluminum nitrate hydrate and water, when employed in accordance with the present invention is a much more efficient nitrating agent than aqueous nitric acid. Moreover, the use of aluminum nitrate hydrate and water in accordance with the present invention has an additional advantage over dilute nitric acid in that the hydrate is more concentrated in nitrate content and therefore requires a smaller vessel and less heat input for reaction.

As can be seen from Example 111, the nitration of methylcyclopentane in conjunction with naphtha gave an unexpectedly high selectivity and high yield; While it is not possible to unequivocally explain this result, it is believed that when the process of'the present invention is effected upon a mixture of organic compounds, one of which is relatively easy to nitrate, the nitration of such compound is facilitated since the compounds that are more difficult to nitrate serve as a butter and prevent undesirable side reactions which serve to decrease the selectivity.

The run set forth in the table involving undiluted aluminum nitrate hydrate as the nitrating agent demonstrates its unfitness for this purpose. Thus, the nitration reaction proceeded out of control with very high resultant temperatures and pressures. In direct contradistinction, when nitration was efiected in accordance with the present invention, smooth operation with a total absence of sudden temperature and pressure surges was achieved.

Under the conditions set forth abovea reaction time of about one hundred and fifty minutes appears to be optimum. Longer reaction times, such as reaction times of five hundred (500) minutes decrease the selectivity. The use of autoclaves and short reaction times such as a thirty (30) minute residence times proved to be inadequate ExampleIV A naphthenic hydrocarbon mixture of petroleum origin was nitrated in accordance with the process of the present invention,

The distribution of hydrocarbons in the charge and in the end products was as follows:

Charge Product Pounds Material Compo- Oompo- Converted sition sltion Methylcyelopentane 61 48 13 Cyelohexane 27 24 3 N. hexane 4 4 Dimethylpentane 5 5 0 Benzene 3 3 0 Nitronaphthenes -1 18 wt. gain by Dinitronaphthenes 7 reactlon It will be seen from the foregoing that the conversion was derived largely from the cycloparafiins under these conditions of reaction.

The nitromethylcyclopentane may be separated from the nitrocyclohexane by contacting the nitration products with a hot solution of caustic. The nitromethylcyclopentane is insoluble in alkali as it is a neutral compound.

The nitrocyclohexane, however, exists in two desrnotropic forms, the aci-form of which is acidic and is therefore soluble in the hot alkali solution, forming a soluble sodium salt in such solution.

Such sodium salt is readily hydrolyzed to cyclohexanone, which can be oxidized to adipic acid or reduced to cyclohexanol by means well known to those skilled in this art.

Thus, distillation of the nitration product set forth in Example IV produced a 75% yield of mononitro cycloparaflins containing six carbon atoms. Such nitro cycloparafiins were extracted with a Weight percent aqueous potassium hydroxide solution.

The caustic extract was acidified with concentrated hydrochloric acid to yield 9 weight percent of ketones (based upon the mononitro cycloparafi'ins containing six carbon atoms). The ketones were a mixture of cyclohexanone and Z-methylcyclopentano-ne. These compounds can be separated by fractional distillation, cyclohexanone having a boiling point of 165 C. and Z-methylcyclopentanone a boiling point of 139 C.

The cyclohexanone was then oxidized to adipic acid by contacting it with a concentrated nitric acid solution containing a vanadium pentoxide catalyst.

Alternatively, the cyclohexanone may be reacted with hydroxylamine hydrochloride to form its oxime which may be reacted with concentrated sulfuric acid to yield caprolactam.

.Nitrocyclohexane may be directly converted to caprolactam in about 30% yield by contact with an acid containing catalyst, such as alumina impregnated with phosphoric acid.

t tive.

Example V 400 parts by weight of iso-oetane were reacted with 900 parts by weight of aluminum nitrate nonahydrate containing 10 weight percent of water based on the aluminum nitrate nonahydrate at 250 F. to yield 40% of theory of a nitro derivative.

Example VI 450 parts by weight of cumene were reacted with 900 parts by weight of aluminum nitrate nonahydrate containing 10 weight percent of water based on the aluminum nitrate nonahydrate at 250 F. to yield 50% of theory of a nitro derivative in which the tertiary carbon of the side chain was nitrated; thus nitrating the nonaromatic portion to the 2-nitro-2-phenyl propane deriva- The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

It is claimed:

1. A process for simultaneously synthesizing the mononitro derivative of a non-aromatic hydrocarbon having 5 to 20 carbon atoms and containing a tertiary carbon atom and the mononitro derivative of a non-aromatic hydrocarbon having 5 to 20 carbon atoms and containing a secondary carbon atom from a mixture comprising said hydrocarbons and effecting a separation of the mononitro derivatives, which process comprises contacting said mixture with a mixture of aluminum nitrate nonahydrate and from five to thirty weight percent of water to nitrate each of said hydrocarbons into their mononitro derivatives, contacting said nitrated hydrocarbons with a strong aqueous alkaline solution to dissolve the mononitro derivative of the hydrocarbon having a secondary carbon atom, and separating the undissolved mononitro derivative of the hydrocarbon having a tertiary carbon atom.

2. A process in accordance with claim 1 in which the non-aromatic hydrocarbon having a tertiary carbon atom is methylcyclopentane and the non-aromatic hydrocarbon having a secondary carbon atom is cyclohexane.

3. A nitration process which comprises contacting methylcyclopentane with a mixture of aluminum nitrate nonahydrate and about ten weight percent of water based on the aluminum nitrate nonahydrate to form a mononitro derivative of said methylcyclopentane, at a temperature of between about 220 F. to 280 F.

References Cited in the file of this patent UNITED STATES PATENTS 2,228,261 Ellingboe Jan. 14, 1941 2,511,454 Bishop et a1 June 13, 1950 FOREIGN PATENTS 1,065,032 France Dec. 30, 1953 720,646 Great Britain Dec. 22, 1954 

1. A PROCESS FOR SIMULTANEOUSLY SYNTHESZING THE MONONITRO DERIVATIVE OF A NON-AROMATIC A TERTIARY CARBON 5 TO 2/ CARBON ATOMS AND CONTAINING A TERTIARY CARBON ATOM AND THE MONONITRO DERIVATIVE OF A NON-AROMATIC HYDROCARBON HAVINH 5 TO 20 CARBON ATOMS AND CONTAINING A SECONDARY CARBON ATOM FROM A MIXTURE COMPRISING SAID HYDROCARBONS AND EFFECTING A SEPARATION OF THE MOMONITRO DERIVATIVES WHICH PROCESS CONTACTING SAID MIXTURE WITH A MIXTURE OF ALUMINUM NITRATE NONAHYDRATE AND FROM FIVE TO THIRTY WEIGHT PERCENT OF WATER TO NITRATE EACH OF SAID HYDROCARBONS INTO THEIR MONONITRO DERIVATIVES, CONTACTING SAID NITRATED HYDROCARBONS WITH A STRON AQUEOUS ALKALINE SOLUTION TO DISSOLVE TJE MONONITRO DERIVATIVE OF THE HYDROCARBON HAVING A SECONDARY CARBON ATOM, AND SEPARTING THE UNDISSOLVED MOMONOITRO DERIVATIVE OF THE HYDROCARBON HAVING A TETRIARY CARBON ATOM. 